Helical spring for artificial reverberation devices

ABSTRACT

A HELICAL SPRING FOR ARTIFICIAL REVERBERATION DEVICES IS CONSTRUCTED TO PERFORM TORSIONAL VIBRATION. MOUNTING MEANS ARE CONNECTED TO AND SUPPORTED THE SPRING UNDER INITIAL AXIAL TENSION IN A MANNER SUCH THAT THE SPRING HAS AT LEAST ONE STRAIGHT OR RECTILINEAR PORTION AND AT LEAST ONE CURVED PORTION. THE STRAIGHT PORTION IS EXTENDED UNDER STRESS IN THE DIRECTION OF THE AXIAL TENSION. THE TURNS OF THE CURVED PORTION ARE SPACED APART SUFFICIENTLY TO BE CLEAR OF EACH OTHER.

Feb. 16, 1971 mm. ETAL 3,564,462

HELICAL SPRING FOR ARTIFfECIAL REVERBERATION DEVICES Filed Nor. 25. 1968 FIG. I.

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I ATT RNEYs United States Patent Oilfice US. Cl. 333-30 9 Claims ABSTRACT OF THE DISCLOSURE A helical spring for artificial reverberation devices is constructed to perform torsional vibration. Mounting means are connected to and support the spring under initial axial tension in a manner such that the spring has at least one straight or rectilinear portion and at least one curved portion. The straight portion is extended under stress in the direction of the axial tension. The turns of the curved portion are spaced apart sufiiciently to be clear of each other.

BACKGROUND OF THE INVENTION When it is desired to produce artificial reverberation in electro-acoustic systems, it is customary to include delay means in a path in shunt or parallel relation with the amplification path. These delay lines are designed so that they delay the signal and produce numerous reflections within the delay line, so that the speaker connected to the output of the main amplifier is fed with a signal which preferably is variable in amplitude, causing the speaker to emit a sound pattern which is similar to naturally reverberated sound.

Such reverberation devices are used not only in large electro-acoustic transmission systems but also in electrical and electronic musical instruments, music amplifiers and installations for improving the acoustic qualities of rooms and the like. For these applications, usually only a small space is available for the reverberation device, so that the dimensions of the latter must be minimized.

This requirement is inconsistent with the fact that the three-dimensional dimensions of the delay line must not be less than a certain minimum if the signal to be reverberated is to be delayed sufliciently in the delay line. In connection with the helical springs which are used almost exclusively as delay lines, this requirement means that the springs must have a certain minimum length, and that the quality will be affected adversely if the length is below this minimum.

In a particularly useful system which produces delays of 100-120 milliseconds and is free of flutter echos, so that the reverberation eflfect is much improved, helical springs having a length of about 80 centimeters are required for a frequency range of kilocycles.

Such helical springs, to which torsional vibration is imparted, are made from relatively thin wire, so that they have virtually no stiffness and are not stable in shape. For this reason, a space-saving shape cannot be imparted to the helical springs because they will not retain this shape. In general, these springs are suspended to be extended along a straight line, and are operated in this position. While systems have been proposed in which the 3,564,462 Patented Feb. 16, 1971 spring or springs are freely suspended to extend along a highly curved catenary line, such arrangements are extremely sensitive to shock and can be used only in special cases. Thus, while such reverberation systems having freely suspended springs require less space, the field of application is greatly restricted.

SUMMARY OF THE INVENTION This invention relates to artificial reverberation devices and, more particularly, to helical springs for such devices wherein the above disadvantages are obviated and inherently small reverberation systems may be further reduced in size, if desired.

For this purpose, the invention is directed to a helical spring, for use in artificial reverberation devices, and to an arrangement of such spring in a reverberation system in which the helical spring has at least in part a curved configuration. Torsional vibration is imparted directly to the spring by an electro-dynamic transducer, and the vibration is analogously converted into electric signals. The spring or arrangement is characterized in that the spring, as installed, has straight portions and curved portions. The straight portions are mounted to be axially extended in the direction of tension of the spring. The turns of the curved portions are spaced sufficiently to preclude a contact between individual turns due to the curvature.

In accordance with another feature of the invention, at least at that point where a straight portion of the spring joins a curved portion thereof, a turn of the spring has a correspondingly inwardly bent portion. One of the adjacent turns of the curved portion is drawn out or expanded to extend along a helix having a large pitch, i.'e., along an arc. This expanded turn receives the free end-portion of a stationary mounting element which is secured to one end of a suspension Wire or suspension spring. This suspension Wire or suspension spring extends along the axis of the straight portion of the helical spring and has its opposite end firmly connected to that point of the inwardly bent portion of a spring turn that is disposed on the axis of the spring.

With this arrangement, a straight portion of the spring may be suspended so as to be supported at a plurality of points, as mentioned above.

It is further possible, within the scope of the invention, to provide a very long helical spring with a plurality of bends, so as to accommodate the spring in a plurality of layers rather than in a single plane. This enables the reverberation device to be designed as an extremely compact or space-saving device.

The actuating transducer may be connected to one end of the spring and the pick-up transducer to the opposite end of the spring. Alternatively, both transducers may be connected to one end of the spring or the transducers may be disposed at desired points between the two ends of the spring.

An object of the invention is to provide an improved helical spring for artificial reverberation devices.

Another object of the invention is to provide such a spring which requires much less space than known helical springs for the same use.

A further object of the invention is to provide such a spring which has, at least in part, a curved configuration.

Another object of the invention is to provide such a spring having straight or rectilinear portions and curved portions with the straight portions mounted to be axially extended in the direction of tension of the spring and with the turns of the curved portions being spaced sufliciently to preclude a contact between individual turns due to the curvature.

A further object of the invention is to provide such a spring in which, at least where a straight portion joins a curved portion, one turn has a correspondingly inwardly bent portion and one of the adjacent turns of the curved portion is expanded to extend along a helix having a large pitch.

Another object of the invention is to provide such a spring in which the expanded turn receives the free end portion of a stationary mounting element connected to one end of a suspension wire spring whose opposite end is connected to that point of the inwardly bent turn portions disposed on the axis of the spring, with the suspension wire or spring extending along the axis of the straight portion of the spring.

A further object of the invention is to provide such a spring which may be supported at a plurality of points therealong.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an elevation view of a helical spring, embodying the invention, before its installation in an artificial reverberation device;

FIG. 2 is a somewhat schematic side elevation view illustrating the mounting of the spring; and

FIG. 3 is a somewhat diagrammatic illustration of the overall arrangement of a spring, embodying the invention, in an artificial reverberation device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As will be apparent from the introductory portion of this specification, a helical spring embodying the invention comprises a plurality of portions, at least one of which is extended along a straight line and under initial axial stress, with at least one other portion being mounted with a curved configuration. Before the spring is installed, its turns are spaced apart suificiently to prevent contact between turns of the curved spring portion when the same has its curvature imparted thereto.

Referring more particularly to the drawings, FIG. 1 shows a. spring F embodying the invention, before it is installed. In FIG. 1, it is assumed that spring P will be installed so as to have a U-shaped configuration consisting of two straight portions or legs connected by a curved portion or bight. Those portions of spring F which are axially extended when the spring is installed are illustrated at 1 and 3. Contrary thereto, the turns of the portion 2, which is to follow a curve upon installation, are wound so as to be spaced apart or, alternatively, spring F has been extended with respect to its portion 2 until the desired turn spacing is attained or maintained.

FIG. 2 illustrates how the spring embodying the invention must be suspended in order to enable it to perform torsional vibration and to minimize the distortion of such vibration. To this end, spring F must be deformed further so that a mounting can be connected to the spring at a central point disposed on the axis of the spring. This is accomplished by bending inwardly to the axis of the spring the turn at which the straight portion merges into the curved portion.

As the vibration is torsional, the mounting element should extend as closely as possible to the axis because, in this case the action of any interference on the vibrational behavior of the spring will be minimized. This result is due to the fact that the moments of inertia increase rapidly with the diameter.

As best seen in FIG. 2, a suspension wire or small spring 5, which is as light in weight as possible, is secured to the point 6 where the deformed turn of the spring intersects the axis of the helical spring. The other end of this wire or small'spring is connected to a stationary mounting element 4, which extends into helical spring F. To facilitate accommodation of the mounting element 4 within the helical spring F, a spring turn which is close to the deformed spring turn is drawn out or expanded to extend along an arc, so that there is suflicient space for the assembling tools.

The overall arrangement of an illustrative embodiment of the invention will be apparent from the diagrammatic showing of FIG. 3. For the sake of simplicity, it is assumed that the helical spring, for producing reverberation, is to have a U-shape and that the actuating transducer and the pick-up transducer are connected to opposite free legs of the U.

Thus, actuating transducer 7 is rigidly secured at one end by a holder 8 and, at its other end, imparts torsional vibration to portion 1 of spring F. This portion 1 is extended along a straight line by the mounting 9. The torsional vibration is transmitted by curved portion 2, mounting 10 and extended straight portion 3 to the pick-up transducer 11 which is secured by a rigid mounting 12 in the same manner as the actuating transducer 7.

When very long delay times are desired, so that very long springs must be accommodated, it is suitable to provide a plurality of bends in the spring. In this case, the spring need not be confined to a single plane. This invention provides for the design of reverberation devices which provide for a long delay and require a minimum space, so that the field of application of reverberation devices can be extended.

What is claimed is:

1. A mechanical delay line assembly, for producing artificial reverberation, comprising, in combination, a helical spring arranged to perform torsional vibration; and mounting means connected to and supporting said spring under initial axial tension and in a manner such that said spring has at least one rectilinear portion and at least one-curved portion; said rectilinear portion being extended under stress in the direction of said tension; the turns of said curved portion being spaced apart sufficiently to be clear of each other.

2. A mechanical delay line assembly, as claimed in claim 1, in which said spring includes 'a transitional turn connecting said rectilinear portion to said curved portion, said transitional turn having an inwardly bent portion extending to the axis of said spring; said mounting means being secured to said inwardly bent portion at the axis of said spring.

3. A mechanical delay line assembly, as claimed in claim 2, in which said curved portion has a plurality of turns adjacent to said transitional turn; one of said plurality of turns extending outwardly of the other turns of said curved portion along a helix having a pitch which is substantially larger than that of the others of said plurality of turns, and substantially along an arc; said mounting means including a fixed mounting element having a free end extending into said one of said plurality of turns.

'4. A mechanical delay line assembly, as claimed in claim 3, in which said mounting means includes a suspension element extending along the axis of said rectilinear portion of said helical spring; one end of said suspension'element being secured to said fixed mounting element and the other end of said suspesion element being claim 1, in which said helical spring has a plurality of bends and extends in dififerent planes.

7. A mechanical delay line assembly, as claimed in claim 6, in which said planes are parallel.

8. A mechanical delay line assemby, as claimed in claim 1, including an electro-dynamic transducer connected to said spring for directly imparting torsional vibrations thereto; and an electro-dynamic transducer connected to said spring for converting torsional vibration thereof into electric signals.

9. A mechanical delay line assembly, as claimed in claim 8, in which said transducers are connected to opposite ends of said spring.

References Cited UNITED STATES PATENTS ELI LIEB-BRMAN, Primary Examiner S. CHATMON. JR., Assistant Examiner U.S. Cl. X.R. 84l.24; 1771.6 

